A ram accelerator is a device for accelerating projectiles to extremely high speeds using jet-engine-like propulsion cycles based on ramjet and/or scramjet combustion processes. The device operates by propelling a projectile through a stationary tube filled with a combustible gaseous propellant mixture. The ram accelerator shows great potential in applications involving large payloads, such as non-rocket space launch.
In conventional powder guns, propellant is burned behind the projectile in a breech, generating high pressure gas which expands as it pushes the projectile down the barrel. As the projectile moves faster, the propelling gas must expend more energy to accelerate itself to keep up with the projectile. Once the projectile reaches a critical velocity, the propellant gas exerts only enough force to overcome friction, and thereafter the projectile begins to slow down if the barrel is too long.
Conversely, a ram accelerator works by filling a launch tube (barrel) with propellant to accelerate the projectile. With a properly shaped projectile/tube, a unique propulsive cycle can be initiated in which the projectile compresses and ignites the propellant as it travels through the tube. This results in a combustion pulse being accelerated down the tube, where the combustion pulse is self-synchronized with the tailing end of the projectile. In essence, the projectile rides its own combustion wave down the length of the launch tube, allowing the projectile to accelerate to speeds far greater than can be achieved by a conventional powder gun.